Mayflies Bug Stations, Car Washes in Upper Midwest (Slideshow)

LA CROSSE, Wis. --Kwik Trip gas stations and car washes were among the many businesses affected last week by mayflies, insects that emerge annually from the Mississippi River in the Upper Midwest in swarms that show up on radar like thunderstorms, coat roads and leave behind slimy messes, reported the Associated Press.

Stations in Red Wing, Minn., are still recovering from the mayflies, which flocked to windows, price signs, parking-lot lights and fuel pumps, said a report by The Wall Street Journal. A steady stream of vehicles poured through the Kwik Trip carwash, leaving it reeking of dead bugs.

"The Mississippi River is a great asset, but we don't need the smell of it in the carwash," David Ring, Kwik Trip's community-relations coordinator told the newspaper.

The flies hatch and then spend a year burrowed into the sediment on the bottom of the river that serves as a border between Wisconsin and Minnesota. They emerge the next summer to mate, lay eggs and die, all in less than 48 hours.

The National Weather Service captured a massive swarm on radar last week as the flies came out of the river and drifted north on the wind. The radar system picks up energy reflected off the flies, with the image's intensity reflecting the density of the bugs.

The weather service typically records several swarms each year from June through August. Air and water temperatures have been usually cool this year, helping explain why this emergence was the first big one this summer, said the report.

Attracted by light, mayflies congregate on roads, bridges and other surfaces in piles that can be nearly 2 feet high. Cars crush the flies, releasing liquid in the females' eggs and making roads slick.